Production and disposal of tumor specific antigen in vivo: Relationship of tumor size to appearance of Ag:Ab, free antigen in circulation and onset of refractory state of lymphoid cells to antigen stimulation; Role of immune response in disposal of tumor antigen in normal and irradiated tumor mice; Rate of clearance of tumor antigen from circulation normal, immune, tumor-bearing mice; Nature of serum (Ig) binding tumor antigen; Degradation steps and products of tumor antigen in circulation; and Organ deposition and disposal of tumor antigen. Biological properties of tumor antigens: Capacity of tumor antigen, antigen-antibody complex, or antibody to stimulate or block stimulation of lymphocytes in vitro; Capacity of tumor antigen, antigen-antibody complex, or antibody to block cellular cytotoxicity in vitro; Relationship of lymphocyte stimulation to refractory state and blocking of cytotoxicity; Use of tumor antigen for in vitro immunization of lymphocytes; and Effect of tumor antigen and/or antibody on tumor growth in vivo.